Effect of boundary conditions on shear behaviour of rock joints around tunnel

This paper discusses the influence of boundary conditions on the shear behaviour of rock joint around tunnel. Direct shear tests were performed on replicas of joint surface cast in cement mortar as well as on artificial tension rock joints, under constant normal stiffness (CNS) and constant normal load (CNL) conditions. The servo-controlled shear apparatus was used to apply varying normal loads in response to dilation. The tests were also performed at various initial normal stress levels. Characteristics and source locations of acoustic emissions from the joints during the CNS shear test and the CNL shear test were also investigated. Results showed that plot of shear stress against normal stress under the CNS condition lay between the peak and residual failure envelopes determined from the CNL condition. From the experimental results, three typical shear behaviour models under the CNS condition were suggested. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".